INFLUENCE OF ZINC(II) BINDING ON THE STRUCTURE OF BOVINE ALPHA-LACTALBUMIN

The effect of Zn(II) binding on the structure of bovine alpha-lactalbu min (LA) was investigated. alpha-lactalbumin, a regulatory subunit of lactose synthase, binds Ca(II) and Zn(II) at different sites in a mutu ally non-exclusive manner. The structures of the metal-depleted form o f LA (ape-LA) and Ca(II)-bound LA (hole-LA) have been well characteriz ed. Here, the effect of Zn(II) binding on the structure of hole-LA has been investigated by comparison with the structure of hole-LA and ape -LA using CD and NMR spectroscopy. The CD spectrum of Zn(II)-holo-LA w as similar to that of hole-LA, but the intensity of the negative peak in near-UV region was decreased. Zn(II) binding to hole-LA produced on ly small changes in NMR chemical shifts, but the integral volumes of t he cross-peaks of NOESY signals in cluster II, which is in the vicinit y of Zn(II) binding site, were affected. Zn(II) binding induces a loca l structural change on the hole-LA, but it does not induce a large bac kbone conformational change. (C) Munksgaard 1996.